1. Field of the Invention
The present invention relates to novel olefin polymerization catalysts that have the ability to polymerize a variety of α-olefins in a stereospecific and living fashion.
2. Related Art
The amidinate ligand fragment, —[N(R1)C(R2)N(R3)]—, is a structural component found within a diverse range of mononuclear transition-metal and main-group-metal complexes (Barker, J. and Kliner, M., Coord. Chem. Rev. 133:219–300 (1994); Edelmann, F. T., Coord. Chem. Rev. 137:403–481 (1994)). Synthetic methods available for the incorporation of this group into the coordination sphere of metals, however, still remain quite limited, and these include (1) classical salt elimination using metal halides and alkali-metal amidinates, (2) condensation between metal halides and silyl-substituted amidines, and (3) carbodiimide insertion into metal-carbon bonds. (Coles, M. P., and Jordan, R. F., J. Am. Chem. Soc. 119:8125–8126 (1997); Sita, L. R., and Babcock, J. R., Organometallics 17:5228–5230 (1998); Korerwas, L. A., et al., Organometallics 18:4183–4190 (1999)).
Recently, it was documented that d0 group 4 mono(cyclopentadienyl)metal amidinates of the general formula (η5—C5R5)MXY[N(R1)C(R2)N(R3)] (M=Zr, R═H, Me, X═Y═Me, R═Me) are highly active precatalysts for the stereoselective living polymerization of a wide variety of α-olefins and α,ω-nonconjugated dienes upon activation with a borate cocatalyst, such as [Ph3C][B(C6F5)4] (Jayaratne, K. C. and Sita, L. R. J. Am. Chem. Soc. 122:958–959 (2000); Jayaratne, K. C., et al., J. Am. Chem. Soc. 122:10490–10491 (2000); Keaton, R. J., et al., J. Am. Chem. Soc. 123:6197–6198 (2001)). Further development of these catalysts is nevertheless needed in order to optimize their catalytic potential. Structure/property relationships must be further studied and heterogenization of the class of Ziegler-Natta precatalyst on solid supports must be developed (Hlatky, G. G., Chem. Rev. 100:1347–1376 (2000)). However, this requires derivatives of the amidinate catalysts that are not readily prepared through the conventional methods enumerated above. Therefore, new methods of derivatizing amidinate metallocene catalysts are needed in order to produce more efficient catalysts.